Liquid crystal imaging system

ABSTRACT

An imaging system wherein a liquid crystal composition is placed in an imagewise field. Molecular orientation within the liquid crystal in areas of field provides a visible image.

United States Patent [1 1 Forest et a1.

1 1 LIQUID CRYSTAL IMAGING SYSTEM [75] Inventors: Edward Forest; CarolK. Keller,

both of Rochester, NY.

[73] Assignee: Xerox Corporation, Rochester, N.Y.

[22] Filed: June 16, 1967 [21] Appl. No.: 646,532

[52] US. Cl 96/1 R, 252/408, 350/160 LC [51] Int. Cl. G03g 13/22, G02f1/16 {58] Field of Search 96/1, 1.1, 1.5; 117/37 LX; 252/501 [56]References Cited UNITED STATES PATENTS 3,484,162 12/1969 Clark 355/33,627,408 12/1971 Fergason 350/160 X 3,410,999 11/1968 Fergason et a1.250/435 3,167,607 l/1965 Marks et a1 88/61 3,322,485 5/1967 Williams350/160 FOREIGN PATENTS OR APPLICATIONS 1,484,584 6/1966 France OTHERPUBLICATIONS Zocher, H. and Birstein, J. Beitrage zur Kenntnis DerMesophasen, .l. uber Die Beeinflussung durch Das Elecktrische undMagnetische Feld Zeitschrift fur Physikalishe Chemie, Vol. 142, pt. A,(1929), pp. 186-194.

Vistin, L. K., and Kapustin, A. P., Domains in Liquid Crystals ofSmectic Type," Soviet Physics-Crystalog- 1 Apr. 16, 1974 raphy, Vol. 13,No. 2, SeptemberOctober, 1968, pp. 284-286. I

158th American Chemical Society Annual Meeting, N.Y., N.Y., September7-12, 1969, Abstract of Pa pers, Craftsman Press, Inc., Bladensburg,Md., C011, 72. Liquid Crystals IV, Electro-Optic Effects inP-Alkyloxybenzilidene-p-Amin0a1kylphenones and Related Compounds.

Les Etats Mesomorphes de la Matiere, Friedel, Ann. de Phys. Le Serie, tXVIII (1922) pp. 273-474. Jones et al., Investigation of LargeAreaDisplay Screen Using Liquid Crystals, Westinghouse Research Lab., 12/65,pp. 4, 7, 9, 15, 99, 101, 119.

Harper, Voltage Effects in Caolesteric Liquid Crystals, WestinghouseResearch Labs, 1966, pp. 325-332. Transient Behavior of Domains inLiquid Crystals George H. I-Ieilmeher Journal of Chemical Physics, Vol.44, No. 2, l/15/66.

Domains in Liquid Crystals Richard Williams Journal of Chemical Physics,Vol. 39, No. 1, 7/15/63.

Primary Examiner-Charles E. Van Horn Attorney, Agent, or Firm-James .l.Ralabate; David C. Petre; Richard A. Tomlin [57] ABSTRACT An imagingsystem wherein a liquid crystal composition is placed in an imagewisefield. Molecular orientation within the liquid crystal in areas of fieldprovides a visible image.

17 Claims, 1 Drawing Figure PATENTEDAPR 1 19 3804.6 1 8 INVENTORS EDWARDFOREST BY CAROL K. KELLER Err ORNE Y LIQUID CRYSTAL IMAGING SYSTEMBACKGROUND OF THE INVENTION This invention relates in general to imagingand in particular to a xerographic system.

In the art of xerography according to Carlson, US. Pat. No. 2,297,691,it is usual to employ the simultaneous application of electric field anda pattern of activating radiation on a photoconductive insulating memherto form an electrostatic charge pattern otherwise known as anelectrostatic latent image. This electrostatic latent image then iscapable of being utilized such as, for example, developed by thedeposition of electroscopic material thereon to form a visible image.Customarily, deposition of the electroscopic material is accomplished bycascading the electrostatic image with an electroscopic powder and agranular carrier as described in US. Pat. No. 2,638,416 to Walkup andWise.

Development by means of depositing electroscopic powders on the surfaceof photoconductive members has a disadvantage in that the softerphotoconductors, particularly those based on selenium, are abraded bythe action of the powders on the photoeonductor surface. The abrasiveaction occurs at two stages of conventional xerography: first, duringthe initial cascading, and second, when the powder is removed bybrushing the photoconductive member prior to the members reuse. In adisplay system, that is, where the developed image is viewed directly orwhere light information from the developed image is projected onto ascreen or a fast developing film, the abrasion problem is more severe.In conventional xerography almost all of the electroscopic powder in thedeveloped image is transferred to paper before the insulating surface iscleaned. In a display system, however, all of the electroscopic powderremains on the insulating surface until the cleaning step resulting ingreatly increased abrasion.

SUMMARY OF THE INVENTION It is, therefore, an object of this inventionto provide a system for developing electrostatic images which overcomethe above noted disadvantages.

It is another object of this invention to provide a system fordeveloping an electrostatic image which does not require physicalcontact between the developer and the photoconductive member.

It is another object of this invention to provide a system fordeveloping an electrostatic image which comparatively does not abradethe photoconductive insulating member.

It is another object of this invention to provide a system fordeveloping an electrostatic image which does not require the depositionof the electroscopic powders.

It is another object of this invention to provide a system fordeveloping an electrostatic image which does not require a cleaningstep.

The foregoing objects and others are accomplished in accordance withthis invention by a system comprising placing a liquid crystallinesubstance in the field generated between an electrostatic latent imageand a conductor, or in a field generated by a source of potentialconnected to shaped electrodes whereby the liquid crystalline substanceis strained by the imagewise field in image configuration providing avisible image.

Liquid crystalline substances are those liquids whose molecules, insteadof being randomly distributed such as a gas, are regularly orientedsimilar to the distribution of molecules in a crystalline solid.Normally, substances which exhibit liquid crystalline characteristics doso only in a relatively narrow temperature range; below this temperaturerange they are solids, above the range they are liquids. Customarily,liquid crystalline substances are divided into three classes: smectic,nematie and cholesteric. Mechanically, these substances resemble liquidshaving viscosities ranging from runny glue to solid glass. Optically,they behave like crystals, for example, a typical cholesteric liquidcrystal substance scatters light in symmetrical patterns and refleetsdifferent colors depending on the angle from which it is viewed. Thelight refraction properties of liquid crystals are also sensitive to thetemperature of the liquid crystal. US. Pat. No. 3,114,836 to Fergason,Vogl and Garbuny, for example, utilizes the temperature sensitivity ofliquid crystals in a thermal imaging device. For further information seeThe Mesomorphic State Liquid Crystals in Chemical Reviews, Vol. 57, No.6, December 1957, p. 1049, by G. H. Brown and W. G. Shaw.

By strained is meant that the oriented molecules in the liquid crystalare reoriented. A visual difference between the field strained and theun-strained liquid crystals provides an image. This difference may be adifference in hue such as red, green, blue, etc. or in lightness, i.e.,different shades of grays. The visible image may also result from adifference in reflectance, refraction, or transparency. Alternatively,light information from the visible image may be projected onto a screenor onto a fast developing film. This invention would be particularlyuseful in a rapid recording and display system such as that disclosed inUS. Pat. 3,1 15,075 to Alexander. The insulating member is then removedfrom the system, solvent washed to remove any liquid crystal adhering toit, air-dried, and stored for later use. Preferably, the liquid crystalis separated from the insulating member by a thin walled, opaque,insulating film, thereby preventing contact between the liquid crystaland the insulating member. This eliminates the requirement of solventwashing the insulating member followed by air-drying.

It is also possible to effect reversal imaging, that is, to developuncharged areas of the electrostatic latent image. Reversal imaging maybe accomplished by charging the conductive member to the same potentialas is present on the charged areas of the electrostatic latent image. Inthis embodiment the resultant field is present only between theconductive member and the uncharged areas of the electrostatic imageresulting in straining of the liquid crystalline material aboveuncharged areas of the electrostatic image providing a visible imagewhich is the reverse of the electrostatic latent image.

The electrostatic latent image may be forrned on either an insulating orphotoconductive insulating surface. If a photoconductive insulatingsurface is to be used, care must be taken not to discharge theelectrostatic latent image during display. That is, actinic radiationimpinging on the surface of the photoconductive layer may discharge theelectrostatic latent image before it has been developed and displayed.It may be necessary, therefore, to use light conditions duringdevelopment and display which will not render the photoconductive layerconductive. For example, red light would be suitable for seleniumphotoconductive layers since selenium is not affected by red light.Suitable lighting conditions for various photoconductive layers whichwill not render the photoconductor conductive, may be determined byreferring to graphs of the relative energy of response ofphotoconductors as a function of the wavelength of light used, avoidingwavelengths which result in photoconductor response. See, for example,Xerography and Related Processes by Dessauer and Clark, Focal Press Ltd,1965. Preferably, however, the insulating film which is placed betweenthe liquid crystal and the insulating member is opaque therebyeliminating the requirement of special lighting during development anddisplay.

It should be understood that for the purposes of this disclosure, theterm insulating when used in reference to the surface bearing theelectrostatic image is intended to include photoconductive insulatingmaterials.

Any suitable insulating member may be used. Typical photoconductiveinsulating materials include inorganic photoconductors such as zincoxide; cadmium sulfide; zinc sulfide; lead sulfide; cadmium selenide;selenium; lead iodide and lead chromate; organic photoconductors such astriphenyl amine; 2,4-bis (4,4'-diethylaminophenyl)-l,3,4-oxadiazol;N-isopropyl carbazole; triphenyl pyrrol; 4,5-diphenylimid-azolidinone;1,4-dicyanonaphthalene; Z-mercapto-benzthiazole,2,4-diphenylquinazoline; S-benzideaminoacenaphthalene; and mixturesthereof. These materials may be used as the photoconductive layer bythemselves as a one phase photoconductor or in a suitable binder.Typical binders are polystyrene resins, silicone resins, acrylic andmethacrylic polymers and copolymers and mixtures thereof. Selenium ispreferred because it has excellent sensitivity and the ability toreceive and retain an electrostatic image with comparatively low darkdecay.

Typical non-photoconductive insulating materials known in the art are:non-self-supporting or selfsupporting films of organic resins, plastics,binders including cellulose, cellulosic materials, and insulating resinssuch as lacquer coatings, and resin films and layers including urea andmelamine-type resins, acrylic resins and mixtures thereof.

Any suitable liquid crystal or mixture of liquid crystals may be used.Typical liquid crystals are cholesteric liquid crystals, such asreaction products of cholesterol and inorganic acids such as cholesterylchloride; cholesteryl nitrate; etc., organic esters of cholesterol suchas cholesteryl crotonate, cholesteryl nonanoate; chlesterylchloroformate; cholesteryl linolate; cholesteryl linolenate; cholesteryloleate; cholesteryl erucate; cholesteryl butyrate; cholesteryl caprate;cholesteryl laurate; cholesteryl myristate; and cholesterylclupanodonate; etc.; ethers of cholesterol such as cholesteryl decylether; cholesteryl lauryl ether; cholesteryl oleyl ether; etc.;carbamates and carbonates of cholesterol such as cholesteryl decylcarbonate; cholesteryl oleyl carbonate; cholesteryl heptyl carbamateetc., alkyl amides and aliphatic secondary amines derived from 33-amino-A -cholestene and mixtures thereof; nematic liquid crystals, suchas anisaldazine; p-azoxyphenetole; p-butoxybenzoic acid;p-methoxycinnamic acid; pazoxyanisole and mixtures thereof. A mixturecomprising cholesteryl butyrate and cholesteryl myristate is preferredbecause of its high color sensitivity to an electric field and becauseit exhibits liquid crystal characteristics at a comparatively lowtemperature.

Any suitable transparent conductive electrode may be used. Typicaltransparent conductive materials include:

conductively coated glass such as tin or indium oxide coated glass, andaluminum coated glass, etc., and similar coatings on transparent plasticsubstrates. NESA (a tin oxide coated glass available from the PittsburghPlate Glass Company) is preferred because it is highly transparent andis readily available.

The thin film which is placed between the liquid crystal and theinsulating member may be of any insulating material. Typical insulatingmaterials are: cellulose acetate, cellulose triacetate, celluloseacetate butyrate, polyurethane elastomers, polyethylene, polypropylene,polyesters, polystyrene, polycarbonates, and mixtures thereof. PigmentedType 30 Tedlar, a polyvinylfluoride available from DuPont, is preferredbecause it is readily available in thin films and because it is opaqueand has good insulation qualities.

BRIEF DESCRIPTION OF THE DRAWING The advantages of this improved methodof developing an electrostatic image will become apparent uponconsideration of the detailed disclosure of the invention, especiallywhen taken in conjunction with the accompanying drawing wherein:

The FIGURE shows a sectional side view of a simple exemplary system forcarrying out the process of this invention wherein the liquidcrystalline material has been placed between a photoconductiveinsulating member and a grounded transparent electrode.

Referring now to the FIGURE, a NESA glass plate 1 is prepared by placingon its surface an inert gasket 2. The shallow cup formed by plate 1 andinert gasket 2 is filled with a liquid crystalline material 3. The depthof this cup, i.e., the depth of the liquid crystalline material 3 usedis a function of the composition of the liquid crystal, the temperatureof the liquid crystal, the potential of the electrostatic latent imageand the thickness and insulating properties of thin film 4. Insulatingfilm 4 is placed in contact with liquid crystal 3 and inert gasket 2.Xerographic plate 7 comprising a layer 5 of photoconductive material ona conductive substrate 6 is sensitized by corona charging. Plate 7 isthen exposed to a pattern of light and shadow which causes the charge todrain away from those areas on which light impinges. The remainingsurface charge is an electrostatic latent image. Xerographic plate 7 isbrought into contact with film 4. The molecules in liquid crystal 3 arestrained in field areas providing a visible image viewable through NESAglass plate 1.

DESCRIPTION OF PREFERRED EMBODIMENTS The following examples furtherspecifically illustrate the present invention. The examples below areintended to illustrate various preferred embodiments of the improveddevelopment method. The parts and percentages are by weight unlessotherwise indicated.

In the following examples the charge density of the latent image is suchthat a field of about 2,000 to 4,000 volts is developed across theliquid crystalline layer.

EXAMPLE I A 2 inch square by /8 inch thick NESA glass plate is preparedby placing on its surface a Teflon (polytetrafluoroethylene availablefrom E. I. du Pont de Nemours & Company, Inc.) gasket having overalldimensions about 2 inches square and a cross sectional dimension about0.l millimeter. The NESA glass plate is then grounded. The NESA plateand Teflon gasket are then heated to a temperature of about 130C. andmaintained at about that temperature throughout the experiment by anelectrical radiant energy heater. The about 0.1 millimeter deep cupformed by the Teflon gasket and NESA glass electrode is filled with amixture of about 55 percent cholesteryl benzoate and about 45 percentcholesteryl acetate which is prepared as follows: The mixture of liquidcrystals are placed in an oven and heated to a temperature of about137C. The mixture is then removed from the oven and allowed to cool to atemperature of about 130C. The mixture is then poured onto the NESAglass plate. An approximately 0.05 millimeter thick film of PigmentedType Tedlar is placed in contact with the liquid crystalline materialand the Teflon gasket.

A 2 inch square by 7 8 inch thick Teflon member is corona chargedthrough a grounded metal stencil in image configuration resulting in anelectrostatic latent image on the surface of the insulating member. TheTeflon member containing the electrostatic latent image is then placedin contact with the insulating film. The image is then viewed throughthe NESA plate. This experiment may be carried out under ordinaryincandescent light conditions because the Teflon member is notphotoconductive, hence will not discharge an electrostatic image in thepresence of ordinary light conditions.

EXAMPLE II A 2 inch square by 7 9 inch thick NESA glass plate isprepared by placing on its surface a Teflon (polytetrafluoroethyle neavailable from E. I. du Pont de Nemours & Company, Inc.) gasket havingoverall dimensions about 2 inches square and a cross sectional dimensionabout 0.1 millimeter. The NESA glass plate is then grounded. The NESAplate and Teflon gasket are then maintained at a temperature of about24C. throughout the experiment. The about 0.1 millimeter deep cup formedby the Teflon gasket and NESA glass electrode is filled with a mixtureof about 30 percent cholesteryl butyrate and about 70 percentcholesteryl myristate which is prepared as follows: the mixture ofliquid crystals are placed in an oven and heated to a temperature ofabout 45C. The mixture is then removed from the oven, poured onto theNESA glass plate, and allowed to cool to a temperature of about 24C. Anapproximately 0.05 millimeter thick film of Pigmented Type 30 Tedlar(DuPont) is placed in contact with the liquid crystalline material andthe Teflon gasket.

A 2 inch square by rt; inch thick selenium xerographic plate comprisingan 80 micron selenium photoconductive layer on an aluminum substrate issensitized by corona charging. The xerographic plate is then exposed toa pattern of light and shadow which causes the charge to drain away fromthose areas on which light impinges. The remaining surface charge is anelectrostatic latent image. The xerographic member containing theelectrostatic image is placed under red light conditions in contact withthe film. The image is then viewed through the NESA glass plate underconventional incandescent light conditions.

EXAMPLE III A liquid crystalline substance made of a mixture of aboutone part cholesteryl crotonate and about one part cholesteryl oleate isdissolved in chloroform to make a free flowing solution. This solutionis poured onto the NESA glass plate Teflon gasket arrangement used inExample I except that in this experiment all components are at aboutroom temperature. The chloroform is allowed to evaporate in air leavinga viscous liquid crystal material on the surface of the NESA glassplate. The insulating film of Example I is placed in contact with theliquid crystal and the Teflon gasket. The NESA glass plate is thengrounded. The xerographic member of Example II containing anelectrostatic latent image is then under red light conditions placed incontact with the insulating film. No heating device need be utilized inthis Example since the liquid crystal used in this Example exhibitsliquid crystal characteristics at or near room temperature. The image isthen viewed through the NESA glass plate under conventional incandescentlight conditions.

EXAMPLE IV A 2 inch square by A; inch thick polycarbonate member madefrom the phosgenation of bisphenol A (4,4-dihydroxydiphenyl-2-2-propane) is corona charged through a groundedmetal stencil in image configuration resulting in an electrostaticlatent image on the surface of the insulating polycarbonate member. ATeflon gasket having overall dimensions about 2 inches square by about0.1 millimeter in cross section is placed over an about 2 inch square byVs inch thick NESA glass plate. A mixture of approximately 30 percentcholesteryl butyrate and about percent cholesteryl myristate isdissolved in chloroform to provide a free-flowing solution. The solutionis then poured into the about 0.1 millimeter deep cup formed by the NESAplate and Teflon gasket. The chloroform is allowed to evaporate in air.The insulating film of Example II is then placed in contact with theliquid crystal and Teflon gasket. The NESA plate is then grounded. Thepolycarbonate member containing the electrostatic latent image is thenplaced in contact with the insulating film. The image is then viewedthrough the NESA plate. No heating device need be utilized in thisExample since the liquid crystal used in this Example exhibits liquidcrystal characteristics at room temperature. This experiment may becarried out under ordinary incandescent light conditions because thepolycarbonate member is not photoconductive, hence, will not dischargean electrostatic image in the presence of ordinary light conditions.

EXAMPLE V A 2 inch square by :4; inch thick NESA glass plate is preparedby placing on its surface a Teflon (polytetrafluoroethylene availablefrom E. I. du Pont de Nemours & Company, Inc.) gasket having overalldimensions about 2 inches square and a cross sectional dimension about0.1 millimeter. The NESA glass plate is then grounded. The NESA plateand Teflon gasket are then heated to a temperature of about C. andmaintained at about that temperature throughout the experiment by anelectrical radiant energy heater. The about 0.1 millimeter deep cupformed by the Teflon gasket and NESA glass electrode is filled withp-azoxyanisole which is prepared as follows: the crystals are placed inan oven and heated to a temperature of 140C. The liquid is then removedfrom the oven and poured onto the NESA glass plate. The liquid is thenallowed to cool to the temperature of the NESA glass plate. Anapproximately 0.05 millimeter thick film of Pigmented Type 30 Tedlar isplaced in contact with the liquid crystalline material and the Teflongasket.

A 2 inch square by /8 inch thick polycarbonate member is corona chargedthrough a grounded metal stencil in image configuration resulting in anelectrostatic latent image on the surface of the insulating member. Thispolycarbonate member containing the electrostatic latent image is thenplaced in contact with the insulating film. The image is then viewedthrough the NESA plate. This experiment may be carried out underordinary incandescent light conditions because the polycarbonate memberis not photoconductive, hence, will not discharge an electrostatic imagein the presence of ordinary light conditions.

EXAMPLE VI A 2 inch square by Vs inch thick NESA glass plate is coatedwith p-azoxyanisole as in Example V. An approximately 0.05 millimeterthick film of Pigmented Type 30 Tedlar is placed in contact with theliquid crystalline material and the Teflon gasket. A shaped electrode ismade by vacuum depositing aluminum in image configuration on the surfaceof a 2 inch square by /8 inch thick piece of molded polycarbonate madefrom the phosgenation of bisphenol A(4,4-dihydroxydiphenyl-2-2'-propane). The aluminum image is continuous sothat current will flow to all parts of the image. The polycarbonatemember is then placed on the Tedlar so that the aluminum image contactsthe Tedlar film. The conductive surface of the NESA plate is connectedto the negative terminal of a potential source of 3,000 volts DC andground. The aluminum image is connected to the positive terminal of thepotential source. The image is then viewed through the NESA plate.

EXAMPLE VII A 2 inch square by /4; inch thick NESA glass plate is coatedwith p-azoxyanisole as in Example V. An approximately 0.05 millimeterthick film of Pigmented Type 30 Tedlar is placed in contact with theliquid crystalline material and the Teflon gasket. A second 2 inchsquare by Vs inch thick NESA glass plate is prepared by placing KodakPhotoresist insulator (available from the Eastman Kodak Company ofRochester, New York and described generally as the cinnamate esters ofpolyvinyl alcohol and of cellulose) on it in image configuration. ThePhotoresist coated surface of the NESA plate is placed in contact withthe Tedlar. The liquid crystal coated NESA plate is connected to thenegative terminal of a 2,000 volt DC potential source and ground. Theother NESA plate is connected to the positive terminal of the potentialsource. The image is viewed through the liquid crystal coated NESAplate.

Although specific components and proportions have been stated in theabove description of preferred embodiments of the invention, othertypical materials as listed above if suitable may be used with similarresults. In addition, other materials may be added to the mixture tosynergize, enhance or otherwise modify the properties of the liquidcrystals, electrodes, light sources, and the photoconductive layers. Forexample, the photoconductive layer may be modified so that ordinaryincandescent light will not discharge the electrostatic latent imageformed on the photoconductive layer.

Other modifications and ramifications of the present invention willoccur to those skilled in the art upon a reading of the disclosure.These are intended to be included within the scope of this invention.

What is claimed is:

1. An imaging process comprising:

providing a layer of an imaging composition comprising a material havinga cholesteric liquid crystalline phase, and

providing an imagewise electrical field across said layer while saidmaterial is in the cholesterie liquid crystalline phase to cause animagewise change in the appearance of image portions of said compositionlayer, while the background portions of said composition layer retain anappearance substantially distinguishable from the appearance of theimage portions of said layer.

2. The process of claim 1 wherein said imaging composition comprises amixture of cholesteryl benzoate and cholesteryl acetate.

3. The process of claim 1 wherein said imaging composition comprises amixture of cholesteryl oleate and cholesteryl crotonate.

4. The process of claim 1 wherein said imaging composition comprises amixture of cholesteryl myristate and cholesteryl butyrate.

5. The process of claim 1 wherein said composition comprises a mixtureof cholesteric liquid crystalline material and nematic liquidcrystalline material.

6. The imaging process of claim 1 comprising the steps of:

a. providing a pair of conductive electrode members in spacedrelationship at least one of said members being sufficiently transparentto transmit a change in the appearance of an imaging composition placedbetween said members;

b. placing between said members an imaging composition comprising amaterial having a cholesteric liquid crystalline phase; and

c. applying an electrical field between said conductive electrodemembers while said material is in the cholesteric liquid crystallinephase to cause a change in the appearance of said composition in animagewise configuration.

7. The process of claim 6 wherein at least one of said conductivemembers has an insulating material in image configuration on at leastits surface.

8. The process of claim 6 wherein there is additionally a gasket ofsubstantially electrically insulating material containing the imagingcomposition between the conductive members.

9. The process of claim 6 wherein at least one of said conductiveelectrode members is shaped in an image configuration.

10. The process of claim 9 wherein there is additionally a substantiallyelectrically insulating layer between the conductive mmember in imageconfiguration and the layer of imaging composition.

11. The process of claim 1 comprising:

providing a surface of a photoconductive member having an electrostaticlatent image thereon; and

15. The process of claim 11 wherein the photoconductive member comprisesphthalocyanine dispersed in a binder.

16. The process of claim 11 wherein the photoconductive member compriseszinc oxide dispersed in a binder.

17. The process of claim 11 wherein said composition comprises a mixtureof cholesteric liquid crystalline material and nematic liquidcrystalline material.

2. The process of claim 1 wherein said imaging composition comprises amixture of cholesteryl benzoate and cholesteryl acetate.
 3. The processof claim 1 wherein said imaging composition comprises a mixture ofcholesteryl oleate and cholesteryl crotonate.
 4. The process of claim 1wherein said imaging compositIon comprises a mixture of cholesterylmyristate and cholesteryl butyrate.
 5. The process of claim 1 whereinsaid composition comprises a mixture of cholesteric liquid crystallinematerial and nematic liquid crystalline material.
 6. The imaging processof claim 1 comprising the steps of: a. providing a pair of conductiveelectrode members in spaced relationship at least one of said membersbeing sufficiently transparent to transmit a change in the appearance ofan imaging composition placed between said members; b. placing betweensaid members an imaging composition comprising a material having acholesteric liquid crystalline phase; and c. applying an electricalfield between said conductive electrode members while said material isin the cholesteric liquid crystalline phase to cause a change in theappearance of said composition in an imagewise configuration.
 7. Theprocess of claim 6 wherein at least one of said conductive members hasan insulating material in image configuration on at least its surface.8. The process of claim 6 wherein there is additionally a gasket ofsubstantially electrically insulating material containing the imagingcomposition between the conductive members.
 9. The process of claim 6wherein at least one of said conductive electrode members is shaped inan image configuration.
 10. The process of claim 9 wherein there isadditionally a substantially electrically insulating layer between theconductive mmember in image configuration and the layer of imagingcomposition.
 11. The process of claim 1 comprising: providing a surfaceof a photoconductive member having an electrostatic latent imagethereon; and providing a layer of an imaging composition comprising amaterial having a cholesteric liquid crystalline phase, on or adjacentsaid surface.
 12. The process of claim 11 wherein a substantiallyinsulating layer is present between the photoconductive member and theimaging composition.
 13. The process of claim 11 wherein thephotoconductive member comprises vitreous selenium.
 14. The process ofclaim 11 wherein the photoconductive member comprises phthalocyanine.15. The process of claim 11 wherein the photoconductive member comprisesphthalocyanine dispersed in a binder.
 16. The process of claim 11wherein the photoconductive member comprises zinc oxide dispersed in abinder.
 17. The process of claim 11 wherein said composition comprises amixture of cholesteric liquid crystalline material and nematic liquidcrystalline material.